Such a device is known in particular from the U.S. Pat. No. 4,717,275 (“the '275 patent). The push member incorporates flexible tabs ensuring a radially directed elastic return force for the locking of the push member, which makes it possible to dispense with a metal return spring fitted longitudinally in a standard fashion at the front of the barrel between an inner wall of the barrel and the cartridge. However, the writing implement described in the '275 patent requires that the cartridge be fitted in a mobile support possessing a housing suitable for receiving these flexible tabs. This cartridge support complicates the manufacture of the implement and increases its cost. Moreover, this device means that the push member occupies almost the entire width of the barrel and as a result is fitted behind the ink reservoir at the rear of the barrel.